JP2004189833A5 - - Google Patents

Description

For this reason, in order to improve the heat resistance of a molded article made of polylactic acid, the molded article is heat-treated to crystallize (JP-A-9-12748) or stretched orientation crystallization (JP-A-8-73628). Although it has been proposed, polylactic acid has a problem that crystallization speed is slow and it becomes opaque when heat-treated the molded product, and a method by stretched orientation crystallization produces a transparent heat-resistant sheet, In order to develop sufficient heat resistance, it is necessary to stretch at least twice or more in the longitudinal direction and the transverse direction, which requires not only large and expensive equipment but also difficulty in producing a thick sheet of 350 μm or more. Furthermore, since polylactic acid has a slow crystallization rate, if the draw ratio is high, distortion due to drawing is not eliminated even if heat setting is performed sufficiently thereafter, and heating to a temperature above Tg causes deformation due to release of the distortion.

When ΔP is more than 0.03, the stretching strain of the sheet becomes large, and in the high temperature state exceeding Tg, the deformation due to the release of the stretching strain tends to occur, and the heat resistance is lowered. The preferred range of ΔP is 0 to 0.02, particularly preferably 0.0001 to 0.01, more preferably from 0.001 to 0.005.